1. Field of the Invention
This invention relates to the production of resistant starch. Preferably, this invention relates to the production of resistant starch comprising selecting a reaction temperature, acidifying unmodified starch to a pH, wherein the pH is optimum to convert the unmodified starch to resistant starch when at the reaction temperature, heating the acidified unmodified starch to about the reaction temperature, and maintaining the acidified unmodified starch close to about the reaction temperature until the maximum yield of resistant starch has been obtained while maintaining a whiteness level between about 50 and about 100.
2. Background Art
The present invention relates to a method of producing resistant starch.
Starch is a naturally occurring polymer made up of anhydroglucose units and is obtained by processing plant materials. The plant materials from which starch is derived include, but are not limited to corn, wheat, potato, casava, and rice. Of these plant materials, corn is one of the most commonly used sources for starch in North America.
Starch is used in a wide number of applications, both industrial and private. These uses include food products, papermaking, corrugated boxes, glue, baby powder and textiles. Food products produced from starch are varied and include dextrose, corn syrup, high fructose corn syrup, crystalline dextrose, fructose, xanthan gum, citric acid, lactic acid, sorbitol, lysine, threonine, riboflavin and distilled spirits.
An additional product is resistant starch, which is a name given to starches which are not digested. Resistant starch is an important part of the human diet. It has been shown to promote intestinal regularity, moderate post-prandial blood glucose levels and lower serum cholesterol and triglyceride levels. Resistant starch is obtained by the manufacture of pyrodextrins which are made at low moisture and low pH by the action of heat and a catalyst such as hydrochloric acid to produce a slightly yellow powder.
Improvements in the standard of living and eating habits, among other factors, have resulted in a lengthened average life span. Accordingly, people have become health oriented. Attention has therefore been directed to dietary fibers and oligosaccharides to enhance the functions of foods and livestock feeds in that these materials are known to alleviate constipation and other desired biological regulatory functions. Indigestible substances, like resistant starches, exhibit various modes of behavior on the digestive tracts, producing physiological effects on the living body. First, in the upper digestive tract resistant starches slow the transport of food and delay the absorption of nutrients. Delayed absorption of sugar, for example, suppresses the rise in blood sugar value, consequently lowering insulin requirements. Further, excretion of bile is promoted, diminishing the sterol group in the body thereby lowering the cholesterol level in the serum. Other physiological effects through the endocrine system are also reported.
Another feature of these indigestible substances is they are not digested or absorbed by the digestive tract, including the small intestine and reach the large intestine. On reaching the large intestine, oligosaccharides, dietary fibers and resistant starches are partly acted on by enterobacteria yielding short-chain fatty acids, intestinal gases, vitamins, etc. Acidification of the intestinal environment by the short-chain fatty acids condition the intestine. It has also been reported that when these short chain fatty acids are metabolized, they provide energy and inhibit the synthesis of cholesterol. Therefore, indigestible substances are necessary in obtaining many desirable physiological effects.
Examples of water-soluble indigestible substances include guar gum, glucomannan, pectin and like natural gums which have high viscosity which are difficult to ingest singly in high amounts. The addition of these indigestible substances to processed foods encounters problems in preparing the food and presents difficulties with respect to texture. It is therefore desirable to provide dietary indigestible substances, like resistant starches, which are easy to ingest and are user friendly in preparing processed food.
Starch is used in large quantities in various processed foods as a food material. Useful food materials of these types include starch and starch products such as pregelatinized starch, pyrodextrin and its derivatives, glucose, corn syrup solids and maltodextrin. However, a majority of these starch products are not higher than 5% in the content of indigestible component.
Starch consists primarily of alpha (1→4) and alpha (1→6) glucosidic linkages. It is well known that resistant starches can be prepared by heat-treating a starch at a high temperature, however, the mechanism of resistant starch development is complex. During the initial stages of dextrinization, acid-catalyzed hydrolysis occurs. This is followed by a recombination of the fragments to form branched structures. Specifically, the dextrinization process converts a portion of the normal alpha-1,4 glucosidic linkages to random 1,2-, 1,3- and 1,4-alpha or beta linkages (O. B. Wurzburg, in Modified Starches: Properties and Uses, CRC Press Inc., Boca Raton, Fla. (1986) pp. 33-34).
These branched structures containing the new bonds are not digestible by maltase and isomaltase in the small intestine. This is because the human digestive system effectively digests only alpha 1,4-linkages. The majority of the resistant starch reaches the large intestine and this conforms to the definition of dietary fiber since it is defined as components of plant material in the diet which are resistant to digestion by enzymes produced by human in the small intestine.
Some methods of producing various resistant starches are known in the art. British gum is obtained by heating starch at 135° C. to 218° C. in the absence of acid catalyst for 3 to 8 hours. White dextrin is prepared by heating starch at 79° C. to 121° C. in the presence of acid catalyst for 3 to 8 hours. Yellow dextrin is prepared similarly by heating the starch at 150° C. to 220° C., with the addition of acid catalyst for 6 to 8 hours.
Proportions of glycosidic linkages have been disclosed (J. D. Geerder et al., J. Am. Chem. Soc., 79: 4209 (1957); G. M. Christensen et al., J. Am. Chem. Soc., 79:4492 (1957)). Compositional analysis reveals that the pyrodextrin obtained by heat treating corn starch with hydrochloric acid comprises at least about 57.3% of 1→4 glycosidic linkage fraction, about 2.6% of 1→6 glycosidic fraction, up to about 1.2% of 1→3 glycosidic fraction, about 6.3% of a fraction having both 1→4 and 1→6 linkages and about 20% having other glycosidic linkages.
Tomasik, P. and Wiejak, S., (Advances in Carbohydrate Chemistry, 47: 279-343 (1990)) generally describe the state of the art as to processes for preparing pyrodextrins and resistant starches.
A process for preparing a dextrin containing an indigestible component has been disclosed (Ohkuma et al., U.S. Pat. No. 5,364,652). This disclosure indicated that if the reaction temperature is higher, the resulting product will contain increased amounts of dietary fiber. A process for preparing dextrin that includes a specific pH acid catalysis, a specific heat, and the digestion of the pyrodextrin with a-amylase has been described (Ohkuma et al., U.S. Pat. No. 5,620,873).
In preparation of resistant starch in dextrin, heat, acid, and time are employed to rearrange the molecular structure to form indigestible branched structures. This also results in the development of color due to caramelization reactions. Caramelization reactions are a diverse group of dehydration, fragmentation and polymerization reactions whose reactions are dependent on temperature and pH (R. S. Shallenberger and G. G. Birch, Sugar Chemistry, AVI, Westport, Conn. (1975) pp. 169-177). The dextrinized starch will typically take on a yellow color depending on the specifics of the reaction conditions.
It is preferable that dextrinization products be almost colorless in solution due to the application of dextrin in the food industry. Any color developed in the dextrinization process is not desirable in the final product and is largely removed through subsequent and costly decolorization steps. In order to minimize the costs associated with color removal, a dextrinized starch with low color development would be advantageous.
However, development of resistant starch in dextrin typically occurs contemporaneously with color development. The object however is to manufacture a dextrin with the greatest degree of resistant starch possible while minimizing the objectionable color formation.
In actual operation, the color is measured by a whiteness meter where the higher the number, the more “white” the product. When a process to manufacture resistant starch is designed, it takes into account the target whiteness of the dextrin. The reason for a target whiteness level is that the decolorization steps can only treat a certain amount of color bodies before recharging. In order to keep costs at economic levels, the dextrinized starch must not be too colored. For example, it has been found that by maintaining a whiteness level of 65 or higher, the subsequent decolorization steps result in an end product of sufficient whiteness that is also economically viable.
The object of the dextrinization process would therefore be to produce a dextrin containing the highest amount of resistant starch possible while maintaining a whiteness of at least 65. Other whiteness targets can be used but they would need either more, or less, equipment to remove color depending on whether it has a lower whiteness (more equipment and materials) or a higher whiteness (less equipment and materials).